The present invention relates to methods of surface-treating workpieces, such as to produce metallurgical coatings, surface alloys, surface heat treatments, or surface etching of the workpieces by sputtering.
A known method for applying surface coatings to workpieces is based on the vacuum arc deposition technique. In this known technique, an electrical discharge is produced between two conducting electrodes in a vacuum ambient, the conduction of the electrical current being by means of a plasma consisting primarily of ionized and neutral species of the electrode material produced by the action of the arc itself at the surface of the electrodes. The presently known techniques are generally based on the application of direct current of low amplitude, typically from 1 to 300 amps and generally use geometries in which the workpiece or substrate is located relatively far from the source or cathode in order to obtain a relatively uniform coating. Such arrangements result in low deposition rates, and therefore the duration of the arcing is usually quite long, typically minutes or hours, in order to produce a coating of significant depth, e.g. at least a few microns. Under these circumstances, heating of the workpiece surface is limited, and the thermal diffusion length is usually large in comparison with the workpiece thickness; the excess heat is usually removed from the workpiece by conduction through the workpiece support, with or without assistance of forced liquid cooling within the support.